Embodiments of the present invention generally relate to engine after-treatment control systems. More particularly, embodiments of the present invention relate to the use of feed-back information with engine after-treatment control systems to provide for closed-loop selective catalytic reduction control.
Selective catalytic reduction (SCR) systems typically are configured to provide one or more catalyst elements that, with the aid of a reductant, covert nitrogen oxides (NOx) in exhaust gases into nitrogen (N2) and water. The reductant, such as, for example, ammonia (NH3), may be injected into the exhaust gas upstream of the SCR catalyst. Typically, engine after-treatment systems attempt to inject a sufficient quantity of reductant into the exhaust gas necessary for the conversion of a predetermined amount of the NOx in the exhaust gas so as to prevent NOx slippage without incurring reductant slippage.
Numerous variable parameters affect the determination of the quantity of reductant that is to be injected into exhaust gases. Further, at least some of these variables may change during operation of the engine, such as, for example, due to changes in engine operating or environmental conditions, or the performance of components within the engine system. Additionally, at least some of these changes may occur relatively rapidly and/or be relatively short in duration, thereby allowing for a relatively short time period for the detection of such changes and to respond accordingly. Conversely, other changes, such as, for example, catalyst aging, may be more gradual, thereby requiring both monitoring over relatively long periods of time and adaptation strategies that are different than strategies that address variations that are more transient in nature. Further, the inability to accurately, and timely, detect and/or predict such shorter and longer term changes or variations may hinder the ability of the after-treatment system to relatively effectively treat NOx in exhaust gases, and thereby may increase the occurrence of NOx slippage or reductant slippage.